1. Field of the Invention
The present invention generally relates to image drawing apparatuses that draw images on display screens, and particularly relates to an image drawing apparatus that is equipped with a function to draw dotted lines.
2. Description of the Related Art
Apparatuses for drawing images and pictures on computer display screens are equipped with various drawing tools, one of which is a function to draw a dotted line of a specified type. Data of a dotted line represents the drawing/skipping of each dot by data “1” and “0”, respectively. Based on this data, dots are drawn in response to data “1”, and are not drawn in response to data “0”, thereby drawing a dotted line.
In related-art dotted-line drawing apparatuses, a thick dotted line is made by drawing identical dotted lines with a horizontal shift by one pixel successively made to each line, or by drawing identical dotted lines with a vertical shift by one pixel successively made to each line. In the related-art dotted-line drawing apparatuses, therefore, broken edges of a thick dotted line extend in the horizontal direction or the vertical direction in the frame buffer regardless of the orientation of the doted line. When a thick dotted line at 45 degrees (relative to the horizontal line) is drawn, the orientation of the line is 45 degrees, but the broken edges of the dotted line end up extending in the horizontal direction or the vertical direction. If the dotted line is a 45-degree line lifted on the right, for example, the broken edges of the dotted line should form a 45-degree line lifted on the left in order to provide natural appearance.
In this manner, the related-art dotted-line drawing apparatuses have a problem in that a thick dotted line ends up having unnatural appearance. In order to provide proper broken edges to the dotted lines, some of the related-art technologies use a method that draws dotted lines by combining basic figures such as triangles and rectangles. Such a method requires a large amount of computation, results in a lengthy processing time and an increase in apparatus size.
Accordingly, there is a need for a dotted-line drawing apparatus that can draw a thick dotted line having natural appearance through simple computation.